A properly configured router should not have any kind of internet-facing login. Most routers than even allow such a thing have it disabled by default (there was a situation maybe 4 or 5 months back where a major ISP... might have been AT&T... shipped some routers with an internet-facing login enabled by default, and there was quite a stink about it).
My judgment of the situation- the chances of that pop-up being able to log keystrokes is incredibly slim, and the chance of anyone being able to make use of your router password to log in to it from the internet is pretty much non-existent. I wouldn't be worried about the situation at all.

I got nothing but a log-in popup . . . maybe someone behind a firewall sent you a msg with a linked image rather than an embedded image ?

That is the popup I was talking about all this while. What do you make of it bro?

I don't think it is necessarily malicious. If someone sent you a message with a company logo or an image that was not embedded in the msg, your [insert program] would probably try to display the image using the link info (inserted by their program when they linked it) to retrieve it. I think the image (little.png) was behind a firewall and when prompted to produce the image the firewall did what it should have and said "OK, log in first".
It may be an exploit in some way but my system was not affected by it. Ran a full AV scan (AVG) and a malware scan (Spybot S&D) and for kicks downloaded McAfee's Stinger which found nothing as well. I think you are good to go . . . =)
I would take the opportunity to strengthen my personal router security since it looked like you had a few more precautions you could take.

Ah, that's even more re-assuring. Thanks old man :D

Personally, I believe it's just a mistake and that there's nothing malicious behind it.
The person who sent the link/image probably didn't realise that the address isn't open to the public, but only accessible to himself when he's logged in.

"Hope for the best, plan for the worst"
It may or may not have been malicious. In any case, anyone who experiences something similar should immediately change the password(s) that might have been compromised.